Oil pressure light question

[mopar 3 B]

Sounds like you're on to something. Could you pull the dizzy and do a inspection of the shaft again before pulling the pan?

Sorry about my last post, talking about a external oil pump. Re-read and see you're working with a small block. Will make an optometrist appt. Tuesday.

Good luck on your findings!

Distributor shaft doesn't drive the pump. The distributor drive gear does. The one that rides the cam gear and turns the oil pump. It needs to be pulled to check pump preasure anyway.

 

[khryslerkid]

Distributor shaft doesn't drive the pump. The distributor drive gear does. The one that rides the cam gear and turns the oil pump. It needs to be pulled to check pump preasure anyway.

Thats what I'm saying.

 

[Wietse]

Blue or red?

The blue one is good.
For general use you can use 243, or 272/278 for high temperature applications.
I've used 243 before in an engine rebuild and never seen a bolt come loose.

Edit: Just read on their website, some of them also provide a good seal around the threads when there is a pressurised fluids behind the bolt.

 

[Steve Garner]

Certainly loose pump parts or a cracked pickup tube are possibilities. Pump failures other than a stuck relief valve are extremely rare. In order for gear or rotor clearances to increase enough for pressure to drop the much softer bearing parts are already long gone. But, by far the most common cause of an oil pressure loss is a bearing failure. If you have a noise in the bottom end along with an oil pressure loss you want to be taking a good look at the mains and rods when you have the pan off.

 

[Sonny]

Certainly loose pump parts or a cracked pickup tube are possibilities. Pump failures other than a stuck relief valve are extremely rare. In order for gear or rotor clearances to increase enough for pressure to drop the much softer bearing parts are already long gone. But, by far the most common cause of an oil pressure loss is a bearing failure. If you have a noise in the bottom end along with an oil pressure loss you want to be taking a good look at the mains and rods when you have the pan off.

Thanks. I will check if the pump is not loose. I’ve heard road knocks in another car and this isn’t a similar noise. Fingers crossed

 

[Steve Garner]

This may not be a rod knock. A wiped out main has a very different sound. A main usually has a barely audible dull rumble.

 

[mopar 3 B]

You may want to check the crankshaft for a crack at a main journal. If it sounds like a diesel at idle.

 

[Wietse]

OMG...

Were talking poor pump output, not a cracked crankshaft

 

[Steve Garner]

OMG...

Were talking poor pump output, not a cracked crankshaft

Why would we suspect poor pump output?

45 years doing this I've never seen a worn out pump. Except for the rare occasion that the pickup was cracked or the relief stuck open, every instance of low oil pressure I've ever seen was the result of excessive bearing clearance. When you think about it, the pump rotors/gears are steel. The bearings are soft aluminum or babbit. Takes a few thou wear from either one to cause either low output or excessive clearance to drop the oil pressure. What is going to wear first?

 

[mopar 3 B]

OMG...

Were talking poor pump output, not a cracked crankshaft

Check the path of oil flow and get back on that one.

 

[Wietse]

Would that have happened so sudden?
Excessive bearing clearance causes lack of oil pressure but never heard it being so excessive, then again i am still new on these old engines.
Modern day cars oil pump capacity is high enough to compensate for some loses.

 

[Steve Garner]

The low oil pressure is the first sign of a worn bearing or a failure. Happens at times before you notice the noise, especially if it's a main or cam brg. Why does it happen so fast? Won't know that until we find out why it happened. Run it low on oil and drew air is the most common. Ford 400's were notorious for premature main bearing wear.

Yes, there is sufficient capacity to cover a certain amount of increase in clearance. That's why he still has oil pressure. The pump output (volume) can't increase, so the pressure has to drop when the clearance increases.

 

[mopar 3 B]

The low oil pressure is the first sign of a worn bearing or a failure. Happens at times before you notice the noise, especially if it's a main or cam brg. Why does it happen so fast? Won't know that until we find out why it happened. Run it low on oil and drew air is the most common. Ford 400's were notorious for premature main bearing wear.

Yes, there is sufficient capacity to cover a certain amount of increase in clearance. That's why he still has oil pressure. The pump output (volume) can't increase, so the pressure has to drop when the clearance increases.

Or the systems capability to keep the oil on the proper path and oil goes were it isn't supposed to go. Internal leaks are some times hard to find.

 

[Sonny]

Is there anything I should try before I pull the pan?

 

[Sonny]

FYI the pressure loss happened within 10 seconds. Literally from 60 psi to 30 in less than a mile.

 

[mopar 3 B]

FYI the pressure loss happened within 10 seconds. Literally from 60 psi to 30 in less than a mile.

Still long enough to take bearings out and scuff the crank if pressure drops to 0.

 

[HT413]

Is there anything I should try before I pull the pan?

Before you do anything, I would prime it with a priming tool and record the reading. Then after each attempt at repair, prime it again to confirm you’ve fixed the problem before starting the car up.

 

[Steve Garner]

FYI the pressure loss happened within 10 seconds. Literally from 60 psi to 30 in less than a mile.

Sometimes our perception of time can be skewed. At 60 mph a mile takes a minute, 30 mph, 2 minutes. What were the circumstances? Wide open throttle and a hard pull? Cruising along at 50 mph?
If it weren't for the noise my first suspect would be a stuck by-pass if it was in fact 10 seconds. But that only happens when the pressure exceeds relief pressure and opens the valve. Usually an ice cold engine revved up.

Broken cranks are rare, but this has the symptoms. Gently rock the crank from one end, feeling for a bit of free movement (it will be small) and watch the other end.

Once you pull the pan you are relying on visual inspections. Always a good idea to have a good idea of what you're looking for before you do that. Try to isolate the area of the noise. Pull the plug wires one at a time and see if removing the load from any one cyl changes the noise.

 

[Sonny]

Sometimes our perception of time can be skewed. At 60 mph a mile takes a minute, 30 mph, 2 minutes. What were the circumstances? Wide open throttle and a hard pull? Cruising along at 50 mph?
If it weren't for the noise my first suspect would be a stuck by-pass if it was in fact 10 seconds. But that only happens when the pressure exceeds relief pressure and opens the valve. Usually an ice cold engine revved up.

Broken cranks are rare, but this has the symptoms. Gently rock the crank from one end, feeling for a bit of free movement (it will be small) and watch the other end.

Once you pull the pan you are relying on visual inspections. Always a good idea to have a good idea of what you're looking for before you do that. Try to isolate the area of the noise. Pull the plug wires one at a time and see if removing the load from any one cyl changes the noise.

If it’s a stuck valve, how do I check it? Fix it? Replace?

 

[mopar 3 B]

If it’s a stuck valve, how do I check it? Fix it? Replace?

If its a stuck valve a leak down or compression test will find it but doesn't explain the loss of oil pressure.